The subject alkoxysilane cluster compounds produced by the method of the present invention are disclosed in the present inventor's U.S. Pat. No. 3,965,136. This patent describes a method for preparing these compounds by reacting a substituted trihalosilane with a trialkoxysilanol in the presence of an acceptor base, and, optionally, a solvent. The present invention defines critical limitations within such a preparation method in order to minimize competing side reactions and maximize desired product yield.